The present invention is directed toward a wavelength division multiplexed (WDM) ring transmission system having two hubs for providing redundant connections to the WDM ring transmission system for improved protection.
Wavelength division multiplexing (WDM) is being explored as an approach for economically increasing the capacity of existing fiber optic networks. WDM systems typically include a plurality of transmitters, each respectively transmitting optical signals on a designated wavelength or channel. As a result, fiber capacity can be increased by a multiple equal to the number of channels.
WDM systems have been deployed in long distance networks in a point-to-point configuration consisting of end terminals spaced from each other by one or more segments of optical fiber. In metropolitan areas, however, WDM systems having a ring or loop configuration are currently being developed. Such systems typically include a plurality of nodes located along the ring, each node providing a connection to an office building, for example. Each optical signal carried by the ring has a unique wavelength corresponding to a particular destination. Thus, for example, one node may add and drop optical signals having a wavelength of 1552.5 nm, while another node may add and drop optical signals at 1553.3 nm. An optical hub is often positioned at a single location along the ring, providing an interface between the WDM ring and an external network. The hub receives either optical or electrical signals from the (external) network which are destined for one of the nodes coupled to the WDM ring. The hub then emits an optical signal modulated in accordance with the signals received from the network at a wavelength associated with the recipient node. The modulated signal is next sensed at the destination node. This node, in turn, can emit optical signals at the associated wavelength, which are detected by the hub and converted to either optical or electrical signals to be transmitted to the external network.
If the connection between the network and the hub fails, or a fault occurs within the hub itself, the entire WDM ring and all the nodes connected thereto are isolated from the network. Accordingly, there is a need for a fault tolerant WDM ring transmission system which can maintain a reliable connection to an external network through a hub.
Consistent with the present invention, a WDM looped or ringed transmission system is provided including first and second optical hubs coupled along the ring. The first optical hub has first and second input ports, as well as first and second output ports. The first input port is configured to receive a first plurality of optical signals, each at a respective one of a first plurality of wavelengths, and the first output port is configured to output the first plurality of optical signals to a looped optical communication path. The second input port is configured to receive the first plurality of optical signals and a second plurality of optical signals, each at a respective one of a second plurality of wavelengths. In addition, the second output port of the first optical hub is configured to output the second plurality of optical signals.
The second optical hub comprises first and second input ports and first and second output ports. The first input port is configured to receive the second plurality of optical signals from the looped optical communication path, and the second input port is configured to receive the first plurality of optical signals. The first output port is configured to output the second plurality of optical signals, and the second output port is configured to output the first and second pluralities of optical signals to the second input port of the first optical hub.